Production printing systems for high-volume printing typically utilize a production printer that marks a continuous-form print medium (e.g., paper) with a wet colorant (e.g., an aqueous ink). After marking the continuous-form print medium, a dryer downstream from the production printer is used to dry the colorant applied to the continuous-form print medium. Serpentine microwave dryers may be employed as a dryer for a production printing system in some applications.
A serpentine microwave dryer utilizes microwave energy to heat the colorant to cause a liquid portion of the colorant to evaporate, thereby fixing the colorant to the continuous-form print medium. A microwave source directs the microwave energy down a long axis of a waveguide, and a passageway through a short axis of the waveguide is sized to pass the continuous-form print medium through the waveguide. As the continuous-form print medium traverses the passageway, the wet colorants applied to the continuous-form print medium are exposed to the microwave energy and are heated. In a serpentine microwave dryer, the waveguides have a long axis that traverses the width of the print medium. The waveguides are electromagnetically coupled together in a row along a media path of the continuous-form print medium, and are aligned in the same plane.
One problem with serpentine microwave dryers is that the electromagnetic energy through successive waveguides is attenuated along the media path. The result is that waveguides at the end of the row farthest from the microwave source exhibit a lower microwave power than the waveguides at the front closest to the microwave source. This reduces the drying efficiency of the microwave dryer.